DESCRIPTION: The long-term goal of the research in the Stampfer laboratory has been the development and characterization of a model system for the culture of human mammary epithelial cells (HMEC), in order to better understand how growth is controlled in normal HMEC and how these regulatory controls change as a result of immortal and malignant transformation. Dr. Stampfer has defined a number of phenotypic markers which suggest that carcinogen-treated HMEC first undergo a conditional immortalization event, and later, after overcoming a growth crisis, become fully immortalized. This latter process, which the principal investigator calls conversion, occurs when the cells have critically short telomeres. The proposed studies will focus on the mechanism of conversion, with the following questions being addressed. Aim 1. What molecular events underlie the conversion process and how are they interrelated? Attempts will be made to determine if the phenotypic changes that occur during conversion (growth in the presence or absence of TGF beta, telomerase activity, regulation of CDKIs (cyclin-dependent kinase inhibitors) p57 and p27, and c-myc) are coordinately controlled, with particular focus on alterations in c-myc and p57 during GO growth arrest. Additionally, the role of p53 in conversion will be assessed, and a determination will be made whether viral oncogenes, which accelerate conversion, can be used as tools to elucidate the conversion process. Aim 2. Can the conversion process be influenced by external conditions such as media composition? Aim 3. How do fully immortal cells maintain telomere length regulation. These studies will focus on the relationship among telomere length, telomerase activity and p57 expression under normal and perturbed (i.e. antisense telomerase RNA) activity. Additionally, the principal investigator will continue to collaborate with other investigators who wish to work with her cell lines.